The invention described herein arose in the course of, or under, Contract No. W-7405-ENG48 between the United States Department of Energy and the University of California for the operation of the Lawrence Livermore National Laboratory.
In laser isotope separation, a large diameter and long length cylindrical ceramic tube is used to contain the electric discharge which provides excitation for the laser transitions traveling down the tube from a laser source to a target. Typically the tube may be about 3 meters (9.84 feet) in length with an outside diameter of about 8.9 cm. (.about.31/2 inches). The tube must be constructed of a high temperature non-reactive ceramic capable of withstanding operating temperatures as high as 1550.degree. C. without reacting with the metal lasant material, e.g., copper liquid or vapor used as the lasant material.
Forming or fabricating such a laser robe from a single ceramic tube, with any degree of precision in dimensional stability, has been very difficult. Differential shrinkage of the ceramic tube during its formation can result in oval or warped tubes. Furthermore stresses created either during fabrication or during operation can also have a deleterious effect on the dimensional integrity of the ceramic lasing tube. If the inner diameter of the tube does not remain true throughout the entire length of the tube, problems of beam blockage can occur, with a portion of the beam striking the wall, resulting in an energy loss. If the outer diameter of the tube is not maintained, problems can arise in fitting insulation around the tube which is then fitted into a quartz envelope or casing of fixed inner diameter. In the past, such lack of uniformity in the ceramic lasing tube resulted in a need to thin portions of the surrounding insulation to permit installation of the ceramic tube in the insulation. This, in turn has resulted in the formation of cold spots in the laser tube (from such selective thinning of the insulation) resulting in loss of performance of the laser. Dimensional inconsistencies in the inner and outer diameters of the lasing tube also increases the labor cost of assembling other materials around the lasing tube, e.g., insulation, quartz casing, and water-cooled vacuum housing around casing.
Segmented tubes have been previously used in laser technology. For example, Hermann et al. U.S. Pat. No. 3,705,999 discusses the use of oxide-coated metal discs which are rigidly interconnected together for use in a lasing tube; while Solomon et al., in U.S. Pat. No. 3,469,207, discloses the formation of a lasing tube using annular ceramic spacer sections which are brazed together for coaxial alignment. McMahan U.S. Pat. No. 3,668,777 shows an assembly of threaded pyrolytic carbon sections in a laser construction having anisotropic orientation of the carbon sheet from which the sections are formed so that the lasing tube exhibits axial electrical semiconductivity.
It would, however, be desirable to provide a high temperature laser assembly having a dimensionally stable segmented ceramic lasing tube therein wherein the inner and outer diameters of each segment of the lasing tube, as measured from the axis of the tube, would not vary more than .+-.0.25 millimeters (0.010 inches) along the entire length of the tube.